High performance skis are carefully designed in order to give the user maximum control during skiing. This includes designing the skis to cleanly "carve" turns; that is, during the carving of a turn, every point on the edge of the ski is designed to pass over a single point on the snow. In order to accomplish this, skis are shaped with curved edges such that the waist portion of the ski is narrower than the shovel or tail portions of the ski. In addition to the exterior shape of the ski, the structural core of the ski is carefully tailored such that the ski has the ability to smoothly flex over its length during the carving of a turn.
During skiing, a snow ski flexes continuously both in response to irregularities in the snow and in response to the user's movements, such as during turning. Flexing of a fiber-reinforced ski causes the various layers of fiberglass and other materials that make up the body of the ski to shear with respect to each other. Elements of the ski which effect the interlaminar shear of the materials that make up the ski affect the resulting flex of the ski. As discussed above, skis are designed to flex freely over their length and in accordance with certain desired flex patterns. Elements of the ski that interfere with such flex patterns undesirably affect the performance of the ski.
Mounting ski bindings on the upper surface of skis and positioning relatively rigid boots within the bindings are known to interfere with the desired flex patterns of the ski. Ski bindings are typically mounted on the top surface of the narrowed waist portion of the ski through the use of screw-type fasteners that extend through the top surface of the ski downward into the core of the ski. A number of fasteners are typically used to hold both the toe piece and heel piece of the binding to the ski. Each of these fasteners pierce the layers of fiberglass and other materials positioned within the body of the ski. This compresses the layers of the ski together and reduces their ability to shear with respect to each other during flexing of the ski. Furthermore, the positioning of a rigid plastic ski boot between the toe and heel pieces of a ski binding tends to prevent the ski from flexing in the area beneath the ski boot, thus creating an inflexible "flat" spot in the ski. The introduction of a "flat" or relatively inflexible portion to the center of the ski reduces the ability of the ski to flex over its length, thus affecting the ski's ability to carve a smooth turn.
A related problem is the tendency of screw-type fasteners, used to hold the bindings to the ski, to pull out of the ski under the significant stresses commonly encountered during skiing. Metal reinforcing plates, such as those shown in U.S. Pat. Nos. 3,498,626; 3,635,482; 3,671,054; 3,844,576; 3,861,699; 3,901,522; 3,917,298; 3,928,106; 4,349,212; 4,639,009; and 4,671,529, are commonly used to provide a base element within the body of the ski into which the fasteners may be screwed and held. This helps to solve the problem of fastener pullout but increases the problems related to ski flexing, due to the introduction of a very stiff element to the narrowed waist portion of the ski.
A number of prior art patents attempt to deal with the problems associated with mounting bindings on a ski. U.S. Pat. No. 2,560,693 discloses a separate foot plate system for allowing a ski to flex uniformly over its entire length. This foot plate system is screwed directly into the body of the ski at its ends, consequently, the screws which mount the foot plate system to the skis compress the various layers that make up the body of the ski. Furthermore, the foot plate system raises the bindings and boots off of the upper surface of the ski, thus affecting the ski's performance.
U.S. Pat. No. 4,141,570 discloses the use of an elevated platform to allow the ski to flex between platform supports. However, the platforms themselves are screwed into the body of the ski thus creating the same problems described above. U.S. Pat. No. 3,997,178 discloses a cross-country ski having a two-layer core with the uppermost layer of the core consisting of wood having a thickness of at least 1.5 mm at its thickest part. The wood upper layer stiffens and increases the resistance of the ski to bending and also acts to prevent the binding screws which extend through the plate into the core of the foam plastic ski from being torn out during skiing.
Another system that attempts to reduce the problems caused by mounting bindings on a ski is the so-called "Derby Flex" system described in PCT Patent No. CH83/00039. This system comprises an aluminum plate overlying a hard rubber substrate. The aluminum plate spans the narrowed waist portion of a ski and allows ski bindings to be screwed directly through the aluminum plate and into the rubber substrate rather than directly into the core of the ski. The aluminum plate, however, is screwed directly into the ski at each end in order to attach the aluminum plate to the ski. Consequently, the screws mounting the aluminum plate compress the layers of material forming the body of the ski, thus interfering with the interlaminar shear between the layers of the ski. Furthermore, the Derby Flex system raises the bindings and ski boot away from the body of the ski, thus changing the profile and influencing the performance of the ski.
In addition to flexing of the ski, vibrations in the ski affect both the performance and the comfort of the ski during use. A highly vibratory ski is not as responsive in precise turns, especially on icy slopes. In addition, high frequency vibrations in skis, approximately 150 Hz and above, tend to be transmitted through the binding to the ski boot and user.
German Patent No. 3,934,888 discloses a system for reducing shock and vibration between a ski and a ski binding through the use of a damping plug recessed into a chamber in the body of the ski. German Patent No. 3,934,891 discloses the placement of a viscoelastic layer on the top surface of a ski in between the ski and binding. The binding screws extend through the viscoelastic layer and into the structural layers which make up the body of the ski.
One goal of the present invention is to reduce the effects of the mounting of ski bindings and ski boots on a ski upon the flex patterns of the ski. A related goal is to reduce the transmission of shock and vibration between a ski and a ski binding and ski boot mounted thereon. The present invention achieves this goal without changing the side profile of the ski or adding additional mounting plates to the top of the ski.